A bedding foundation or "box spring" generally has a wood base frame upon which springs are mounted. Coil or torsion bar springs are typically used. The frame has wooden side and end rails defining its perimeter, with wood or metal cross rails, or spans, extending between the side rails. The feet of the springs are typically stapled directly to the frame members, or inserted in slots on metal spans.
A metal box spring frame assembly is shown in Surletta et al., U.S. Pat. No. 3,431,073, which discloses end and side rails of metal connected together by corner elements into a rectangular frame. A plurality of metal spans is connected by a flange and groove arrangement to the side members and shaped to retain a plurality of springs.
Mizelle, U.S. Pat. No. 4,470,584, discloses a box spring assembly which utilizes channel-shaped metal cross rails having horizontal spring mounting slots. Still another type of foundation is disclosed in Gauthier, U.S. Pat. No. 3,302,220, where the supporting frame consists of a lightweight metal framework with triangular corner-brackets. Norman, U.S. Pat. No. 3,657,749, shows a substantially planar rail-type construction used as a border for the spring assembly.
Although metal foundations are generally described above, the use of rigid metal end and side rails has not seen commercial acceptance. Cost of metal vs. wood has been a factor, particularly since metal rails must generally be formed from light stock to be at all cost-effective and saleable. Attachment of the metal rails together is also a problem, as is attachment of cloth and ticking to the metal rails.